What Types of PC Memory are There to Choose From?

So you're looking for PC memory to upgrade your system with, but
aren't quite sure what you're looking for. Hopefully we can help
you with some information about the various types of memory that
are available to choose from.

The first type of memory to see widespread use is the 72-pin SIMM(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=72pin).
Unlike the 30-pin SIMM that preceded it, the 72-pin version had
a 32-bit data bus, requiring only one or two memory modules to fill
the system's data bus, as opposed to the four or eight 30-pin SIMMs
that had been required before that. The 72-pin SIMM these days will
need to be installed in pairs, as almost all systems have a 64-bit
data bus, and come in sizes ranging from 8MB to 128MB of memory.
So if you want to add only 128MB of PC memory to your system, remember
to get two 64MB
memory modules(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=64M-EDO).
Otherwise, make sure what type of 72-pin SIMM you need, as there
are two formats - FPM (Fast Page Mode) and EDO (Extended Data Out),
and not all motherboards will work with both types, not to mention
that you will need to make sure that if you are adding RAM to your
system, you install the same type as is already being used.

The replacement for the 72-pin SIMM PC memory is the 168-pin SDRAM(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=168pin).
The 168-pin SDRAM has a few advantages over the 72-pin SIMM, but
the greatest advantage is the 64-bit data bus used by the memory.
This means that each module communicates with the system's data
bus without needing to pair memory together, and allows for upgrading
the memory one piece at a time. In addition, SDRAM operates at a
higher speed then 72-pin SIMMs, operating at 66MHz(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=PC66),
100MHz(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=PC100)
or 133MHz(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=PC133).
The size of memory available in 168-pin SDRAM varies widely, from
32MB(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=32M-PC100)
up to 1GB(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=1.0G-PC133)
modules. The most common sizes in use these days are 256MB(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=256M-AP133)
and 512MB(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=512M-PC133).

Rambus
RAM(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=184and232)
entered the PC Memory market between SDRAM and the introduction
of DDR memory, in 1999. Rambus operates at 800MHz or 1066MHz by
sends data twice during a clock cycle through a 16-bit bus or 32-bit
bus, as opposed to SDRAM's slower 100MHz or 133MHz sending data
once during a clock cycle through a 64-bit bus. What this means
is that Rambus sends data much more quickly to the system, but has
a much narrower channel to use. If you want to visualize it, Rambus
sends data four times as fast as SDRAM, but only has a two lane
highway. SDRAM moves slower, but has eight lanes to send data on.
This reduces Rambus' speed advantage, and combined with Rambus'
higher cost, both in motherboards that take use Rambus memory and
its own price, limits Rambus' share of the market. With the advance
of SDRAM technology and the emergence of the faster DDR memory,
Rambus has become slower yet more expensive then it's competitors.
Rambus PC memory is still on the market, but generally goes for
a higher price then DDR and DDR2 memory. Rambus memory comes in
sizes ranging from 64MB to 512MB, and must be installed in pairs
if it uses 16-bit memory, or can be installed one at a time if the
Rambus memory uses a 32-bit memory bus. One final thing to note
with Rambus memory is that all sockets that do not have memory in
them must have a continuity spacer in their place, so all memory
sockets are filled with either RAM or spacers.

DDR
memory (http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=184pin)
is the successor to SDRAM PC memory, and like Rambus sends data
twice during a memory clock cycle. This allows DDR to effectively
send twice as much information as SDRAM along the same bus. DDR
memory has come in a number of different speeds, but the highest
official DDR speed is DDR400(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=PC3200),
which operates at 200MHz and can send up to 3.2GB of data per second.
While higher speed DDR RAM is available, it is generally only useful
if you plan to overclock your system, which is setting components
like the memory and processor to run above their rated speed, which
risks causing damage to your memory and other parts of your computer.
DDR memory comes in sizes ranging from 128MB(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=128M-PC3200)
to 2GB(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=2.0G-PC3200ER)
per module. It is still a fairly common type of memory, though DDR2
has since replaced it as the current standard for PC memory.

DDR2(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=240pin)
memory is the current standard in the PC industry, and as the name
suggests, is an extension of DDR memory. DDR2 operates by setting
the data bus twice as fast as the memory, thus allowing the memory
to send more information in the same time period. While this initially
gave DDR2 higher internal latencies then DDR, technology has advanced
to the point where DDR2 memory operates faster and with the same
latencies. DDR2 memory ranges in speed from 400MHz to 800MHz, and
modules range in size from 256MB(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=256M-PC2-4200&Category_Code=240pin)
all the way up to 4GB(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=4.0G-PC2-4200ER&Category_Code=PC2-4200)
modules.

So which type of PC memory is right for you? Though there are a
few general tips, such as any computer purchased in the last year
or two is likely to use DDR2 memory, probably the best way to find
out is to use our memory checking utility below. If you're currently
using the computer you plan to upgrade, click the 'Check Your Computer'
button and it will report back to you what type of RAM your computer
uses, how many slots it has and which are open, and also the best
options for adding RAM. If you know the model of the system you
want to upgrade, you can enter it in the model number field and
find the best upgrades for that model of computer. Finally, feel
free to take a look around - in addition to PC memory, we also carry
memory for Macintosh computers as well as memory
cards(http://www.oempcworld.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=Flash)
for cell phones, PDAs, and cameras.